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        <title>JsonPathReader</title>
        <link rel="stylesheet" href="../../../../../css/component-usage.css" type="text/css"/>
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    <body>
        <p>
        	The JsonPathReader Controller Service, parses FlowFiles that are in the JSON format. User-defined properties
        	specify how to extract all relevant fields from the JSON in order to create a Record. The Controller
        	Service will not be valid unless at least one JSON Path is provided. Unlike the
        	<a href="../org.apache.nifi.json.JsonTreeReader/additionalDetails.html">JsonTreeReader</a> Controller Service, this
        	service will return a record that contains only those fields that have been configured via JSON Path.
        </p>
        
        <p>
        	If the root of the FlowFile's JSON is a JSON Array, each JSON Object found in that array will be treated as a separate
        	Record, not as a single record made up of an array. If the root of the FlowFile's JSON is a JSON Object, it will be
        	evaluated as a single Record.
        </p>
        
        <p>
        	Supplying a JSON Path is accomplished by adding a user-defined property where the name of the property becomes the name
        	of the field in the Record that is returned. The value of the property must be a valid JSON Path expression. This JSON Path
        	will be evaluated against each top-level JSON Object in the FlowFile, and the result will be the value of the field whose
        	name is specified by the property name. If any JSON Path is given but no field is present in the Schema with the proper name,
        	then the field will be skipped.
        </p>
        
		<p>
			This Controller Service must be configured with a schema. Each JSON Path that is evaluated and is found in the "root level"
			of the schema will produce a Field in the Record. I.e., the schema should match the Record that is created by evaluating all
			of the JSON Paths. It should not match the "incoming JSON" that is read from the FlowFile.
		</p>


		<h2>Schemas and Type Coercion</h2>
		
		<p>
			When a record is parsed from incoming data, it is separated into fields. Each of these fields is then looked up against the
			configured schema (by field name) in order to determine what the type of the data should be. If the field is not present in
			the schema, that field is omitted from the Record. If the field is found in the schema, the data type of the received data
			is compared against the data type specified in the schema. If the types match, the value of that field is used as-is. If the
			schema indicates that the field should be of a different type, then the Controller Service will attempt to coerce the data
			into the type specified by the schema. If the field cannot be coerced into the specified type, an Exception will be thrown.
		</p>
		
		<p>
			The following rules apply when attempting to coerce a field value from one data type to another:
		</p>
			
		<ul>
			<li>Any data type can be coerced into a String type.</li>
			<li>Any numeric data type (Byte, Short, Int, Long, Float, Double) can be coerced into any other numeric data type.</li>
			<li>Any numeric value can be coerced into a Date, Time, or Timestamp type, by assuming that the Long value is the number of
			milliseconds since epoch (Midnight GMT, January 1, 1970).</li>
			<li>A String value can be coerced into a Date, Time, or Timestamp type, if its format matches the configured "Date Format," "Time Format,"
				or "Timestamp Format."</li>
			<li>A String value can be coerced into a numeric value if the value is of the appropriate type. For example, the String value
				<code>8</code> can be coerced into any numeric type. However, the String value <code>8.2</code> can be coerced into a Double or Float
				type but not an Integer.</li>
			<li>A String value of "true" or "false" (regardless of case) can be coerced into a Boolean value.</li>
			<li>A String value that is not empty can be coerced into a Char type. If the String contains more than 1 character, the first character is used
				and the rest of the characters are ignored.</li>
			<li>Any "date/time" type (Date, Time, Timestamp) can be coerced into any other "date/time" type.</li>
			<li>Any "date/time" type can be coerced into a Long type, representing the number of milliseconds since epoch (Midnight GMT, January 1, 1970).</li>
			<li>Any "date/time" type can be coerced into a String. The format of the String is whatever DateFormat is configured for the corresponding
				property (Date Format, Time Format, Timestamp Format property). If no value is specified, then the value will be converted into a String
				representation of the number of milliseconds since epoch (Midnight GMT, January 1, 1970).</li>
		</ul>
		
		<p>
			If none of the above rules apply when attempting to coerce a value from one data type to another, the coercion will fail and an Exception
			will be thrown.
		</p>
		
		

		<h2>Examples</h2>

        <p>
        	As an example, consider a FlowFile whose content contains the following JSON:
        </p>
        
        <code>
        <pre>
[{
    "id": 17,
    "name": "John",
    "child": {
        "id": "1"
    },
    "siblingIds": [4, 8],
    "siblings": [
        { "name": "Jeremy", "id": 4 },
        { "name": "Julia", "id": 8}
    ]
  },
  {
    "id": 98,
    "name": "Jane",
    "child": {
        "id": 2
    },
    "gender": "F",
    "siblingIds": [],
    "siblings": []
  }]
		</pre>
        </code>
        
        <p>
    		And the following schema has been configured:
        </p>
        
        <code>
        <pre>
{
	"namespace": "nifi",
	"name": "person",
	"type": "record",
	"fields": [
		{ "name": "id", "type": "int" },
		{ "name": "name", "type": "string" },
		{ "name": "childId", "type": "long" },
		{ "name": "gender", "type": "string" },
		{ "name": "siblingNames", "type": {
			"type": "array",
			"items": "string"
		}}
	]
}
        </pre>
        </code>
        
        <p>
        	If we configure this Controller Service with the following user-defined properties:
        	
        	<table>
        		<tr>
        			<th>Property Name</th>
        			<th>Property Value</th>
        		</tr>
    			<tr>
    				<td>id</td>
    				<td><code>$.id</code></td>
    			</tr>
    			<tr>
    				<td>name</td>
    				<td><code>$.name</code></td>
    			</tr>
    			<tr>
    				<td>childId</td>
    				<td><code>$.child.id</code></td>
    			</tr>
    			<tr>
    				<td>gender</td>
    				<td><code>$.gender</code></td>
    			</tr>
    			<tr>
    				<td>siblingNames</td>
    				<td><code>$.siblings[*].name</code></td>
    			</tr>
        	</table>
        </p>
        
		<p>
			In this case, the FlowFile will generate two Records. The first record will consist of the following key/value pairs:

        	<table>
        		<tr>
	    			<th>Field Name</th>
	    			<th>Field Value</th>
				</tr>
    			<tr>
    				<td>id</td>
    				<td>17</td>
    			</tr>
    			<tr>
    				<td>name</td>
    				<td>John</td>
    			</tr>
    			<tr>
    				<td>childId</td>
    				<td>1</td>
    			</tr>
    			<tr>
    				<td>gender</td>
    				<td><i>null</i></td>
    			</tr>
    			<tr>
    				<td>siblingNames</td>
    				<td><i>array of two elements: </i><code>Jeremy</code><i> and </i><code>Julia</code></td>
    			</tr>
			</table>
		</p>
		
		<p>
			The second record will consist of the following key/value pairs:

        	<table>
        		<tr>
        			<th>Field Name</th>
        			<th>Field Value</th>
        		</tr>
    			<tr>
    				<td>id</td>
    				<td>98</td>
    			</tr>
    			<tr>
    				<td>name</td>
    				<td>Jane</td>
    			</tr>
    			<tr>
    				<td>childId</td>
    				<td>2</td>
    			</tr>
    			<tr>
    				<td>gender</td>
    				<td>F</td>
    			</tr>
    			<tr>
    				<td>siblingNames</td>
    				<td><i>empty array</i></td>
    			</tr>
			</table>
		</p>
		
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